Scraper assembly for process vessels

ABSTRACT

A rotating scraper blade, for use in a process vessel containing liquid, is driven by a hollow shaft whose ends are sealed off from the liquid, thereby to entrap air in the hollow interior of the shaft and provide a buoyant effect on the scraper assembly. There may be additional supports for the blade, in the form of pipes whose ends are similarly sealed off from the liquid, and secured to the driving shaft.

Elmte States Patent 1 11 3,731,339

Addison 1 May 8, 1973 [54] SCRAPER ASSEMBLY FOR PROCESS [56] ReferencesCited VESSELS UNITED STATES PATENTS 1 lnventori Christopher Addison,Media, 3,405,760 10/1968 Smith ..165/94 Del. 2,809,815 10/1957 Born 1..259/109 713474 71955 R d ..2 9D] 4 [73] Assignee: Sun Oil Company ofPennsylvania, ea 5 G 3 Philadelphia Primary Examiner-Leon G. Machlin[22] Filed: Sept 29, 1971 AttorneyGeorge L. Church et al.

[21] App1.No.: 184,862 57 ABSTRACT A rotating scraper blade, for use ina process vessel [52] U.S. Cl. ..l5/246.5, 259/109, 165/94 containingliquid, is driven by a hollow shaft whose [51] Int. Cl ..F28g 3/12 endsare sealed off from the liquid, thereby to entrap [58] Field of Search..15/246.5, 104.05, air in the hollow interior of the Shaft and Providea 15/104.09,104.1, 104.13;259/l82, 104, 103, 109, 110, DIG. 34; 165/109,94; 23/285 buoyant effect on the scraper assembly. There may beadditional supports for the blade, in the form of pipes whose ends aresimilarly sealed off from the liquid, and secured to the driving shaft.

4 Claims, 2 Drawing Figures SCRAPER ASSEMBLY FOR PROCESS VESSELS Thisinvention relates to scraped surface process equipment, and moreparticularly to a scraper assembly for use in process vessels.

In certain processes, such as heat exchange, mixing, crystallization,precipitation, etc., the process vessel is filled with a liquid (amother liquor) from which solids settle out. The solids which thussettle out are scraped from the inner wall of the vessel by means of oneor more (generally, a pair) of rotating scraper blades which are coupledby means of springs to a central (axial) rotating drive shaft, thecylindrical process vessel being positioned in most cases with itslongitudinal axis substantially horizontal. In large diameter vessels,the blades are coupled by means of springs to separate support memberswhich in turn are secured to the central shaft.

The central shaft is mounted in bearings at each end of the vessel, andgenerally also at intermediate points along its length. The greater theweight of the scraper, the greater the number of intermediate bearingswhich are required. Ordinarily, spider-supported bearings (wherein theshaft bearings are located at the center or hub of a spoke-likearrangement) are inserted in the vessel to support the scraper atintermediate points along its length. These bearings are difficult toinstall and provide unscraped surfaces where solids deposit, withresultant obstruction of the flow; this undesirably increases thepressure drop through the vessel. It may be observed that any reductionin scraper weight will lessen the need for such bearings, which is adesirable result. In addition, the weight of the scraper causes bearingwear; here also, any reduction in scraper weight will reduce bearingwear, again a desirable result.

An object of this invention is to provide a novel scraper assemblyconstruction.

Another object is to provide a supporting arrangement for scrapers whichreduces the effective weight of the scraper assembly.

A further object is to perform the foregoing objects in a relativelysimple yet efficient and effective manner.

A detailed description of the invention follows, taken in conjunctionwith the accompanying drawing, wherein:

FIG. I is a generally longitudinal cross-section of a portion of aprocess vessel incorporating this invention; and

FIG. 2 is a transverse section taken along line 2--2 of FIG. 1.

Referring now to the drawing, a substantially cylindrical processvessel, denoted generally by the numeral I, is positioned with itslongitudinal axis extending horizontally, by way of example. This vesselis elongated, and only a portion of its total length is illustrated inFIG. 1. During operation of the process, vessel 1 contains a liquid 2.Inside vessel 1, there is mounted a scraper assembly, denoted generallyby numeral 3. The scraper assembly may for example weigh about 15 poundsper foot of length, and may comprise a plurality of sections one ofwhich is illustrated in FIG. 1.

Scraper assembly 3 comprises a pair of scraper blades 4 and 5 locatedessentially diametrically opposite each other with respect to vessel 1and adapted to scrape the inner cylindrical wall of the vessel. For

scraping the vessel wall, the blades 4 and 5 are rotated about thelongitudinal axis (horizontal in FIG. I) of vessel 1; by way of example,the direction of rotation of the blades might be clockwise, viewed inFIG. 2. A central hollow shaft 6, mounted axially of vessel 1, is usedto support and rotate the blades 4 and 5 about the vessel longitudinalaxis. For an elongated vessel 1 as illustrated, the shaft 6 is made upin sections which are welded together end-to-end, with a suitableuniversal joint between adjacent sections. According to this invention,each section of the hollow shaft 6 is sealingly welded at its oppositeends to respective plates such as 7 and 8, so that the hollow interiorof each section of the shaft is sealed ofi from the liquid 2, thereby toentrap air in the interior of the shaft; at the same time, the platessuch as 7 and 8 mechanically couple together adjacent sections of theelongated shaft 6. For example, a universal joint such as previouslyreferred to would be coupled to the section of shaft 6 to the left ofplate 7, and another universal joint would be coupled to the section ofshaft 6 to the right of plate 8 (FIG. 1). The rigid coupling and sealingplates 7, 8, etc. are spaced, parallel, and extend essentiallytransversely within vessel 1.

In some cases, the blades 4 and 5 would be mounted on leaf springsconnected to the central shaft 6. However, for large diameter equipmentsuch as that illustrated, secondary supports, in the form of tubular(hollow) support members 9 and 10, are utilized. The elongated supportmembers 9 and 10 extend parallel to shaft 6, on respective oppositesides thereof. Viewed in elevation, as in FIG. 2, the plates 7, 8, etc.are substantially rectangular in shape. One end of member 9 is sealinglywelded to plate 7, and the opposite end of this member is sealinglywelded to plate 8; thus, the hollow interior of member 9 is sealed offfrom the liquid 2, thereby to entrap air in the interior of this member,and member 9 is mechanically secured to driving shaft 6 through plates 7and 8. Similarly, one end of member 10 is sealingly welded to plate 7,and the opposite end of this latter member is sealingly welded to plate8; thus, the hollow interior of member 10 is sealed off from the liquid2, thereby to entrap air in the interior of this member, and member 10is mechanically secured to driving shaft 6 through plates 7 and 8.

A plurality of longitudinally-spaced leaf springs 11 are utilized tocouple scraper blade 4 to member 9, for support and rotation thereby.One end of each spring 11 is attached to scraper blade 4, and the otherend of each spring is attached to member 9 (see FIG. 2).

A plurality of longitudinally-spaced leaf springs 12 are utilized tocouple scraper blade 5 to member 10, for support and rotation thereby.One end of each spring 12 is attached to scraper blade 5, and the otherend of each spring is attached to member 10.

As the shaft 6 rotates about its own axis (which is collinear with thelongitudinal axis of vessel 1), it carries the plates 7, 8, etc. aroundwith it, rotating the members 9 and 10, which (through springs 11 and12) drive in turn the scraper blades 4 and 5. The blades 4 and 5, asthey rotate about the longitudinal axis of vessel l scrape the innerwall of this cylindrical vessel.

As previously described, the hollow shaft 6, and also the tubularsupport members 9 and 10, are sealed off from the liquid 2, so that airis entrapped in the hollow interiors of all of the hollow members (orpipes) 6, 9, and 10. This air entrapped in the members (which areentirely surrounded by the process liquid 2, within vessel 1) provides abuoyant effect (which may be thought of as a flotation effect) on thescraper assembly which reduces its effective weight, due to the weightof the liquid 2 (process fluid) displaced. An effective weight reductionof 25 percent can easily be obtained, depending upon the process liquid.This reduction in the effective weight of the scraper assembly reducesbearing wear, and also reduces the need for internal bearings (i.e.,bearings located at intermediate points along the length of the scraperassembly).

It has been stated that the improved scraper assembly of this inventionreduces the need for internal bearings (spider bearings). Whether suchspider bearings can be completely eliminated will depend on the lengthof the scraped vessel, the density of the liquid 2, and the design ofthe springs 11 and 12. For very long scrapers, some spider bearings willprobably still be required, since the flotation effect or buoyant effect(resulting from the use of this invention) does not equal 100 percent ofthe weight of the scraper assembly.

The foregoing description has assumed that the shaft 6 is made up insections which are welded together. This is a common type ofconstruction, and it enables plates 7, 8 to seal off all three hollowmembers 6, 9, and 10. If this type of construction is not used,seal-welded plugs can easily be inserted in the hollow members, to sealthem off from the liquid 2.

in petroleum processing, processes in which the scraped surfaceequipment of this invention could be used, by way of example, are MEKde-waxing and solvent de-oiling, wherein wax crystals settle out from anoil/solvent liquid phase.

The invention claimed is:

1. A scraper assembly for use in scraping the inner wall of asubstantially cylindrical process vessel containing a liquid, comprisinga scraper blade adapted to scrape the inner cylindrical wall of saidvessel, a hollow shaft mounted axially of said vessel for supporting androtating said blade about the vessel longitudinal axis, the interior ofsaid shaft being sealed off from said liquid, thereby to entrap air inthe hollow interior of such shaft; an elongated support member extendingparallel to said shaft, means securing said support member to saidshaft, and means coupling said blade to said support member, saidsupport member being hollow and being sealed off from said liquid,thereby to entrap air in the hollow interior of such member.

2. Assembly of claim 1, wherein the means coupling the blade to thesupport member comprises a leaf spring mounted between the blade and thesupport member.

3. A scraper assembly for use in scraping the inner wall of asubstantially cylindrical process vessel containing a liquid, comprisinga pair of scraper blades adapted to scrape the inner cylindrical wall ofsaid vessel, a hollow shaft mounted axially of said vessel forsupporting and rotating said blades about the vessel longitudinal axis,the interior of said shaft being sealed off from said liquid, thereby toentrap air in the hollow interior of such shaft; a pair of elongatedsupport members extendin parallel to said shaft on respective oppositesides t ereof, means securing each of said support members to saidshaft, and means coupling each of said blades to a respective one ofsaid support members, each of said support members being hollow andbeing sealed off from said liquid, thereby to entrap air in the hollowinterior of each such member.

4. Assembly of claim 3, wherein the means coupling each blade to arespective support member comprises a leaf spring mounted between eachblade and a respective support member.

1. A scraper assembly for use in scraping the inner wall of asubstantially cylindrical process vessel containing a liquid, comprisinga scraper blade adapted to scrape the inner cylindrical wall of saidvessel, a hollow shaft mounted axially of said vessel for supporting androtating said blade about the vessel longitudinal axis, the interior ofsaid shaft being sealed off from said liquid, thereby to entrap air inthe hollow interior of such shaft; an elongated support member extendingparallel to said shaft, means securing said support member to saidshaft, and means coupling said blade to said support member, saidsupport member being hollow and being sealed off from said liquid,thereby to entrap air in the hollow interior of such member.
 2. Assemblyof claim 1, wherein the means coupling the blade to the support membercomprises a leaf spring mounted between the blade and the supportmember.
 3. A scraper assembly for use in scraping the inner wall of asubstantially cylindrical process vessel containing a liquid, comprisinga pair of scraper blades adapted to scrape the inner cylindrical wall ofsaid vessel, a hollow shaft mounted axially of said vessel forsupporting and rotating said blades about the vessel longitudinal axis,the interior of said shaft being sealed off from said liquid, thereby toentrap air in the hollow interior of such shaft; a pair of elongatedsupport members extending parallel to said shaft on respective oppositesides thereof, means securing each of said support members to saidshaft, and means coupling each of said blades to a respective one ofsaid support members, each of said support members being hollow andbeing sealed off from said liquid, thereby to entrap air in the hollowinterior of each such member.
 4. Assembly of claim 3, wherein the meanscoupling each blade to a respective support member comprises a leafspring mounted between each blade and a respective support member.